French Pat. No. 2,219,060 (SOBREAL) describes a process for effecting this type of wrapping which generally comprises the steps of:
unrolling and feeding a thermally weldable web from at least one roll of the web material;
feeding the product to be wrapped against the taut web;
pressing the product perpendicularly to the path of the web so that the article will entrain the web and the web will wrap around the article;
effecting on the web two parallel welds, the first connecting the ends of the stretch of the web surrounding the article and the second being spaced from the first and connecting stretches of the web supplied to the wrapping location and a stretch of web by which the web was tensioned; and
cutting the web between the two weld seams.
In this wrapping method, the weld seam proximal to the article closes the sheath while the other weld seam, formed with spacing from the first and more remote from the article, serves to join the stretches of the web separated from the sheath by the cutting operating into a single stretch so that the next article can be pressed thereagainst and the process repeated.
The web is thus wrapped around each product and nevertheless has the separated portions formed upon liberation of the packaged product from the web in a substantially continuous state so that another length can be drawn off to wrap the next product or article.
French Pat. No. 2,219,060 also describes a machine for carrying out this process and comprising principally:
a feeder for advancing the articles to be wrapped;
one or more rolls of a thermally weldable web carried by an upper portion of the machine;
a fixed double-jaw lower welding member;
a vertically movable upper double-jaw welding member;
a cutting tool associated with one of the welding members;
a roller deflector around which the web passes in the course of unrolling from one of the rolls; and
a draw-down device located below the lower welding member and serving to draw the end of the web formed by the small lost portion of the latter downstream of the cutting action at each wrapping operation;
the second weld here holds this lost portion to the oncoming portion of the web.
The machine also provided with means for receiving and supporting the article during the course of wrapping.
In the use of machines of this type, one can feed cylindrical products of various lengths to be wrapped. If the machine is equipped at its upper portion with a plurality of rolls of the web, it is easy to see that the rolls can carry webs of different widths adapted to wrap, for example, products to two or three different lengths.
While the machine as described can be operated effectively for wrapping articles of a uniform length, problems are encountered upon a change in length of the product to be wrapped since the supply of a web of a width different from a previous web width poses problems.
Because of the manner in which the described machine functions, the transition between one web width and other web width requires that the web previously unrolled be rolled back up and that the new web be unrolled.
In practice this operation has been effected manually and represents a costly intervention in the automatic operation of the machine because of the time required for the manual changeover.
Up to the present time, the problem of automating the changeover of the web has not been resolved at least in part because of difficulties encountered in guiding the free end of a web to be unrolled or to be rolled back up.
Because the web, especially when it is a film, has a very light free end, even ordinary air currents are capable of deflecting the web or deforming it and prevent it from arriving at the desired location in the machine when the web is fed without guidance.
Of course, it is possible to imagine that one can grip the free end of the web in pincers or the like and draw it with such pincers along the desired path.
However, such devices are highly complex, costly and prone to failure. The problem is all the more acute since it is necessary to provide pincers with a variable spacing to adapt to the different widths of the web to be used.